The cellular interactions and biochemical mechanisms underlying immunosuppression in a murine model of chronic lymphocytic leukemia (CLL) will be studied with the long term goal of understanding and eventually treating the immune incompetence accompanying CLL in humans. The immune defects in mice bearing the B cell leukemia (BCL1) will be further explored with emphasis on distinguishing between responses to antigens encountered prior to disease from those antigens encountered after development of leukemia. The cell type(s) responsible for suppression will be identified definitively with particular attention to distinguishing among macrophages, dendritic cells and NK cells and the possible participation of T cells in the induction sequence. A role for factors released by tumor cells, T cells or suppressor cells will be explored and if factors are involved, we will attempt to purify and characterize them. We will assess the relationship of suppression to tumor regression.